FIG. 1 illustrates a block diagram 100 of a prior art I/O subsystem 110. The prior art I/O subsystem 110 has an upstream port 120 and the downstream ports 1-4 130, 140, 150 and 160. The I/O data is routed among the upstream port 120 via the communication links 125 and 170 and the downstream ports 1-4 130, 140, 150 and 160 via their respective communication links 135, 145, 155 and 165.
While waiting for packets from each of the downstream ports 1-4 130, 140, 150 and 160, the upstream port 120 typically remains in a full power-up state. This causes the I/O subsystem to consume high power even when the upstream port 120 is not servicing any of the downstream ports 1-4 130, 140, 150 and 160.